The family of ISIS hostage and U.S. aid worker Peter Kassig released a YouTube video Saturday asking his captors to show mercy and free him .

Referring to him as Abdul-Rahman -- a first name his family says he took , having converted to Islam while being held hostage -- father Ed Kassig said : `` We implore his captors to show mercy and use their power to let our son go . ''

Peter Kassig , 26 , first went to the Middle East as a U.S. soldier and returned as a medical worker , feeling compelled to help victims of war .

His mother , Paula , addressed her son in the video : `` We are so very proud of you and the work you have done to bring humanitarian aid to the Syrian people , '' she said .

`` Most of all , know that we love you , and our hearts ache for you to be granted your freedom so we can hug you again and then set you free to continue the life you have chosen , the life of service to those in greatest need , '' she added .

The couple noted they were releasing the video on the same day of Islam 's Eid al-Adah or the Festival of Sacrifice , when Muslims slaughter lambs , goats , sheep and cattle and distribute the meat to the poor and their families . The holiday coincides with the end of the hajj pilgrimage and commemorates Allah 's sparing Abraham from sacrificing his son Ishmael .

A native of Indiana , Peter Kassig founded Special Emergency Response and Assistance , a nongovernmental organization aiding Syrians fleeing the civil war there .

Since 2012 , he delivered food and medical supplies within and outside Syria and provided trauma care and training , his family said .

But on October 1 , 2013 , he was `` detained '' on his way to Deir Ezzor in eastern Syria while performing a project for SERA , his family said .

Peter Kassig 's life was threatened Friday in an ISIS video that showed the apparent beheading of British aid worker Alan Henning .

In a statement Friday , Kassig 's parents , Ed and Paula Kassig of Indianapolis , confirmed that their son was being held hostage by ISIS but provided no other details on his abduction . They had maintained silence about his capture since he was taken hostage in 2013 .

`` The Kassig family extends our concern for the family of Alan Henning , '' Kassig 's parents said . `` We ask everyone around the world to pray for the Henning family , for our son , and for the release of all innocent people being held hostage in the Middle East and around the globe . ''

Joined the Army in 2006

Kassig 's journey began when he joined the U.S. Army Rangers in 2006 and deployed to Iraq in 2007 . He was honorably discharged for medical reasons after a brief tour and returned to the United States to study political science and train for 1,500-meter races . But something was n't right .

`` I was going to school with kids who look the same , were the same age as me , but we were n't the same , '' he said . `` I wanted more of a challenge , a sense of purpose . ''

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In 2010 , Kassig took time off and began his certification as an emergency medical technician .

In the two years that followed , he fell in love , got married and quickly divorced . Devastated and heartbroken , he went back to school , but he could n't shake his depression .

`` I needed a game-changer , '' he said .

He decided he would head to Beirut , follow the situation in Syria and try to help . So , on his spring break this year he packed his medical kit and flew into the Lebanese capital .

The next two weeks were filled with eye-opening misadventures as Kassig began to scratch the surface of the complexities of the Syrian conflict and the Middle East as a whole .

Founded a humanitarian aid organization

`` I had learned enough to know that I did n't know anything , '' he said .

After finishing the semester back in the United States , he returned to Lebanon , only this time with a plan .

`` The way I saw it , I did n't have a choice . This is what I was put here to do . I guess I am just a hopeless romantic , and I am an idealist , and I believe in hopeless causes . ''

Kassig then founded SERA , and in summer 2013 he moved its base of operations to Gaziantep , Turkey .

Kassig 's family said SERA was dedicated to providing first-response humanitarian aid for refugees fleeing the widening civil war in Syria .

`` I am not a doctor . I am not a nurse , '' he said in the 2012 interview . `` But I am a guy who can clean up bandages , help clean up patients , swap out bandages , help run IVs , make people 's quality of life a little bit better . This is something for me that has meaning , that has purpose . ''

Converted to Islam

Kassig 's family said he converted to Islam while being held hostage and now goes by Abdul-Rahman .

The family said they understand , `` from speaking to former hostages , that Kassig 's faith has provided him comfort during his long captivity . ''

While working in hospitals , some of those Kassig helped treat were rebel fighters , all who vowed they would return to the battlefield as soon as they could .

Others were the innocent victims of a spiraling conflict .

One patient , 24-year-old Louliya , said she and her three children were run over by a military jeep as they tried to escape the Syrian military siege of their village . Her spinal cord was crushed , leaving her unable to move from the neck down . She was smuggled across the border to Lebanon for surgery .

She smiled bravely but was unable to stop the tears from rolling down her face .

`` All I want is to be able to hold my children in my arms again , '' she said softly , trying but failing to imitate the cradling of a child .

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He bonded with doctors , patients

Kassig said his direct exposure to what was something of an alien conflict and culture before transformed his perspective .

`` There is this mentality from where I come from back home that I have a little bit of a problem with , '' he said . `` I do n't want to get on a political soap box , but at the same time we have to think about why as a country we choose to help certain people and not others .

`` We have to think about why we just chalk up the Middle East -LSB- as -RSB- this complex enigma that we will never understand because they are so different from us . But at the end of the day , they are really not . It 's just about whether or not you 're willing to go out on a limb and understand something , '' he said .

`` Peter can tell the American people who we are , '' said Marwan , a Syrian nurse he worked with . `` We are not what the regime says we are -- terrorists and al Qaeda . Peter knows we are good people , who love joking and laughter . We just want to live . ''

Kassig was struck by the resilience of the Syrians he met , by their ability to smile and somehow joke even in the darkest of circumstances .

`` This is real , and it 's scary stuff , and it 's sad what is happening to people here , '' he said . `` People back home need to know about it , they need to know . Sometimes you got ta take a stand , you got ta draw a line somewhere . ''

When outrage is n't enough

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Ed and Paula Kassig urge ISIS to release their son

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Peter Kassig changed his first name to Abdul-Rahman when converting to Islam

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`` We implore his captors to show mercy , '' his father says on videotaped message

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`` Most of all , know that we love you , '' his mother says to son